Silane-containing carboxy-terminated polymers

ABSTRACT

Polymers are functionalized at chain ends thereof with silane-containing carboxyl groups of the formula (I) 
                         
where R 1  and R 2  are the same or different and are each an H, alkyl, alkoxy, cycloalkyl, cycloalkoxy, aryl, aryloxy, alkaryl, alkaryloxy, aralkyl or aralkoxy radical; R 3  and R 4  are the same or different and are each an H, alkyl, cycloalkyl, aryl, alkaryl or aralkyl radical; and A is a divalent organic radical.

The invention relates to end group-functionalized polymers, and to thepreparation and use thereof.

Important properties desirable in tyre treads include good adhesion ondry and wet surfaces, low rolling resistance and high abrasionresistance. It is very difficult to improve the skid resistance of atyre without simultaneously worsening the rolling resistance andabrasion resistance. A low rolling resistance is important for low fuelconsumption, and high abrasion resistance is a crucial factor for a longservice life of the tyre.

Wet skid resistance and rolling resistance of a tyre tread dependlargely on the dynamic/mechanical properties of the rubbers which areused in the blend production. To lower the rolling resistance, rubberswith a high resilience at higher temperatures (60° C. to 100° C.) areused for the tyre tread. On the other hand, for improving the wet skidresistance, rubbers having a high damping factor at low temperatures (0to 23° C.) or low resilience in the range of 0° C. to 23° C. areadvantageous. In order to fulfil this complex profile of requirements,mixtures of various rubbers are used in the tread. Usually, mixtures ofone or more rubbers having a relatively high glass transitiontemperature, such as styrene-butadiene rubber, and one or more rubbershaving a relatively low glass transition temperature, such aspolybutadiene having a high 1,4-cis content or a styrene-butadienerubber having a low styrene and low vinyl content or a polybutadieneprepared in solution and having a moderate 1,4-cis and low vinylcontent, are used.

Anionically polymerized solution rubbers containing double bonds, suchas solution polybutadiene and solution styrene-butadiene rubbers, haveadvantages over corresponding emulsion rubbers in terms of production oftyre treads with low rolling resistance. The advantages lie, inter alia,in the controllability of the vinyl content and of the associated glasstransition temperature and molecular branching. In practical use, thesegive rise to particular advantages in the relationship between wet skidresistance and rolling resistance of the tyre. Important contributionsto energy dissipation and hence to rolling resistance in tyre treadsresult from free ends of polymer chains and from the reversible buildupand degradation of the filler network formed by the filler used in thetyro tread mixture (usually silica and/or carbon black).

The introduction of functional groups at the end of the polymer chainsand/or start of the polymer chains enables physical or chemicalattachment of these ends and/or starts of the polymer chains to thefiller surface. This restricts the mobility thereof and hence reducesenergy dissipation under dynamic stress on the tyre tread. At the sametime, these functional groups improve the dispersion of the filler inthe tyre tread, which can lead to a weakening of the filler network andhence to further lowering of the rolling resistance.

For this purpose, numerous methods for end group modification have beendeveloped. For example, EP0180141A1 describes the use of4,4′-bis(dimethylamino)benzophenone or N-methylcaprolactam asfunctionalizing reagents. The use of ethylene oxide andN-vinylpyrrolidone is also known from EP0864606A1. A number of furtherpossible functionalizing reagents are detailed in U.S. Pat. No.4,417,029. Methods for introducing functional groups at the start ofpolymer chains by means of functional anionic polymerization initiatorsare described, for example, in EP0513217A1 and EP0675140A1 (initiatorswith a protected hydroxyl group), US20080308204A1 (thioether-containinginitiators) and in U.S. Pat. No. 5,792,820, EP0590490A1 and EP0594107A1(alkali metal amides of secondary amines as polymerization initiators).

The carboxyl group, as a strongly polar, bidentate ligand, can interactparticularly well with the surface of the silica filler in the rubbermixture. Methods for introducing carboxyl groups along the polymer chainof diene rubbers prepared in solution are known and are described, forexample, in DE2653144A1, EP1000971A1, EP1050545A1, WO2009034001A1. Thesemethods have several disadvantages, for example that long reaction timesare required, that the functionalizing reagents are converted onlyincompletely, and that an alteration of the polymer chains occurs as aresult of side reactions such as branching. Moreover, these methods donot enable particularly effective functionalization of the ends of thepolymer chain.

The introduction of carboxyl groups at the chain ends of diene rubbershas likewise been described, for example in U.S. Pat. No. 3,242,129, byreaction of the anionic ends of the polymer chain with CO₂. This methodhas the disadvantage that the polymer solution has to be contacted withgaseous CO₂, which is found to be difficult because of the highviscosity and the resultant poor mixing. In addition, coupling reactionswhich are difficult to control occur as a result of reaction of morethan one end of the polymer chain at the carbon atom of the CO₂. Thiscoupling can be avoided by sequential reaction of the carbanionic endsof the polymer chain first with ethylene oxide or propylene oxide,followed by reaction of the ends of the polymer chain which are nowalkoxidic with a cyclic anhydride (U.S. Pat. No. 4,465,809). Here too,however, there is the disadvantage that gaseous and additionally verytoxic ethylene oxide or propylene oxide has to be introduced into thehigh-viscosity rubber solution. Furthermore, reaction of the alkoxidicchain ends with the cyclic anhydride forms hydrolysis-prone ester bondswhich can be cleaved in the course of workup and in the course of lateruse.

Especially silanes and cyclosiloxanes having a total of at least twohalogen and/or alkoxy and/or aryloxy substituents on silicon are of goodsuitability for end group functionalization of diene rubbers, since oneof said substituents on the silicon atom can be readily exchanged in arapid substitution reaction for an anionic diene end of the polymerchain and the further aforementioned substituent(s) on Si is/areavailable as a functional group which, optionally after hydrolysis, caninteract with the filler of the tyre tread mixture. Examples of silanesof this kind can be found in U.S. Pat. No. 3,244,864, U.S. Pat. No.4,185,042, EP0778311 A1 and US20050203251A1.

These silanes generally have functional groups which are bonded directlyto the silicon atom or bonded to Si via a spacer and can interact withthe surface of the silica filler in the rubber mixture. These functionalgroups are generally alkoxy groups or halogens directly on Si, andtertiary amino substituents bonded to Si via a spacer. Disadvantages ofthese silanes are the possible reaction of a plurality of anionic endsof the polymer chain per silane molecule, elimination of troublesomecomponents and coupling to form Si—O—Si bonds in the course of workupand storage. The introduction of carboxyl groups by means of thesesilanes has not been described.

WO2012/065908A1 describes 1-oxa-2-silacycloalkanes as functionalizingreagents for introduction of hydroxide end groups in diene polymers.These 1-oxa-2-silacycloalkanes do not have the disadvantages of thesilanes described in the above paragraph, such as reaction of aplurality of anionic ends of the polymer chain per silane molecule,elimination of troublesome components and coupling to form Si—O—Si bondsin the course of workup and storage. However, these functionalizingreagents also do not enable the introduction of carboxyl groups at theends of the polymer chain.

The problem addressed was therefore that of providingcarboxyl-terminated polymers which do not have the disadvantages of theprior art and more particularly enable utilization of the goodreactivity of silanes having anionic ends of the polymer chain.

This problem is solved through the proposal of end group-functionalizedpolymers having, at the end of the polymer chain, a silane-containingcarboxyl group of the formula (I)

where

-   R¹, R² are the same or different and are each an H, alkyl, alkoxy,    cycloalkyl, cycloalkoxy, aryl, aryloxy, alkaryl, alkaryloxy, aralkyl    or aralkoxy radical which may contain one or more heteroatoms,    preferably O, N, S or Si,-   R³, R⁴ are the same or different and are each an H, alkyl,    cycloalkyl, aryl, alkaryl or aralkyl radical which may contain one    or more heteroatoms, preferably O, N, S or Si,-   A is a divalent organic radical which, as well as C and H, may    contain one or more heteroatoms, preferably O, N, S or Si.

Preferably, the inventive end group-functionalized polymers may be inthe form of carboxylates having end groups of the formula (II):

where

-   R¹, R² are the same or different and are each an H, alkyl, alkoxy,    cycloalkyl, cycloalkoxy, aryl, aryloxy, alkaryl, alkaryloxy, aralkyl    or aralkoxy radical which may contain one or more heteroatoms,    preferably O, N, S or Si,-   R³, R⁴ are the same or different and are each an H, alkyl,    cycloalkyl, aryl, alkaryl or aralkyl radical which may contain one    or more heteroatoms, preferably O, N, S or Si,-   A is a divalent organic radical which, as well as C and H, may    contain one or more heteroatoms, preferably O, N, S or Si,-   n is an integer from 1 to 4,-   M is a metal or semimetal of valency 1 to 4, preferably Li, Na, K,    Mg, Ca, Zn, Fe, Co, Ni, Al, Nd, Ti, Sn, Si, Zr, V, Mo or W.

Preferred polymers for preparation of the inventive endgroup-functionalized polymers are diene polymers, and diene copolymersobtainable by copolymerization of dienes with vinylaromatic monomers.

Preferred dienes are 1,3-butadiene, isoprene, 1,3-pentadiene,2,3-dimethylbutadiene, 1-phenyl-1,3-butadiene and/or 1,3-hexadiene.Particular preference is given to using 1,3-butadiene and/or isoprene.

The vinylaromatic comonomers may, for example, be styrene, o-, m- and/orp-methylstyrene, p-tert-butylstyrene, α-methylstyrene, vinylnaphthalene,divinylbenzene, trivinylbenzene and/or divinylnaphthalene. Particularpreference is given to using styrene.

These polymers are preferably prepared by anionic solutionpolymerization or by polymerization by means of coordination catalysts.In this context, coordination catalysts are understood to meanZiegler-Natta catalysts or monometallic catalyst systems. Preferredcoordination catalysts are those based on Ni, Co, Ti, Zr, Nd, V, Cr, Mo,W or Fe.

Initiators for anionic solution polymerization are those based on alkalimetals or alkaline earth metals, for example methyllithium,ethyllithium, isopropyllithium, n-butyllithium, sec-butyllithium,pentyllithium, n-hexyllithium, cyclohexyllithium, octyllithium,decyllithium, 2-(6-lithio-n-hexoxy)tetrahydropyran,3-(tert-butyldimethylsiloxy)-1-propyllithium, phenyllithium,4-butylphenyllithium, 1-naphthyllithium, p-tolyllithium and allyllithiumcompounds derived from tertiary N-allylamines, such as[1-(dimethylamino)-2-propenyl]lithium,[1-[bis(phenylmethyl)amino]-2-propenyl]lithium,[1-(diphenylamino)-2-propenyl]lithium,[1-(1-pyrrolidinyl)-2-propenyl]lithium, lithium amides of secondaryamines, such as lithium pyrrolidide, lithium piperidide, lithiumhexamethyleneimide, lithium 1-methylimidazolidide, lithium1-methylpiperazide, lithium morpholide, lithium dicyclohexylamide,lithium dibenzylamide, lithium diphenylamide. These allyllithiumcompounds and these lithium amides can also be prepared in situ byreaction of an organolithium compound with the respective tertiaryN-allylamines or with the respective secondary amines. In addition, itis also possible to use di- and polyfunctional organolithium compounds,for example 1,4-dilithiobutane, dilithium piperazide. Preference isgiven to using n-butyllithium and sec-butyllithium.

In addition, it is possible to use the known randomizers and controlagents for the microstructure of the polymer, for example diethyl ether,di-n-propyl ether, diisopropyl ether, di-n-butyl ether, ethylene glycoldimethyl ether, ethylene glycol diethyl ether, ethylene glycoldi-n-butyl ether, ethylene glycol di-tert-butyl ether, diethylene glycoldimethyl ether, diethylene glycol diethyl ether, diethylene glycoldi-n-butyl ether, diethylene glycol di-tert-butyl ether,2-(2-ethoxyethoxy)-2-methylpropane, triethylene glycol dimethyl ether,tetrahydrofuran, ethyl tetrahydrofurfuryl ether, hexyltetrahydrofurfuryl ether, 2,2-bis(2-tetrahydrofuryl)propane, dioxane,trimethylamine, triethylamine, N,N,N′,N′-tetramethylethylenediamine,N-methylmorpholine, N-ethylmorpholine, 1,2-dipiperidinoethane,1,2-dipyrrolidinoethane, 1,2-dimorpholinoethane and potassium and sodiumsalts of alcohols, phenols, carboxylic acids, sulphonic acids.

Such solution polymerizations are known and are described, for example,in I. Franta, Elastomers and Rubber Compounding Materials; Elsevier1989, pages 113-131, in Houben-Weyl, Methoden der Organischen Chemie[Methods of Organic Chemistry], Thieme Verlag, Stuttgart, 1961, volumeXIV/1 pages 645 to 673 or in volume E 20 (1987), pages 114 to 134 andpages 134 to 153, and in Comprehensive Polymer Science, Vol. 4, Part II(Pergamon Press Ltd., Oxford 1989), pages 53-108.

The preparation of the preferred diene homopolymers and diene copolymerspreferably takes place in a solvent. The solvents used for thepolymerization are preferably inert aprotic solvents, for exampleparaffinic hydrocarbons such as isomeric butanes, pentanes, hexanes,heptanes, octanes, decanes, cyclopentane, methylcyclopentane,cyclohexane, methylcyclohexane, ethylcyclohexane or1,4-dimethylcyclohexane, or alkenes such as 1-butene, or aromatichydrocarbons such as benzene, toluene, ethylbenzene, xylene,diethylbenzene or propylbenzene. These solvents can be used individuallyor in combination. Preference is given to cyclohexane,methylcyclopentane and n-hexane. Blending with polar solvents islikewise possible.

The amount of solvent in the process according to the invention istypically in the range from 100 to 1000 g, preferably in the range from200 to 700 g, based on 100 g of the total amount of monomer used.However, it is also possible to polymerize the monomers used in theabsence of solvents.

The polymerization can be performed in such a way that the monomers andthe solvent are initially charged and then the polymerization is startedby adding the initiator or catalyst. Polymerization in a feed process isalso possible, in which the polymerization reactor is filled by additionof monomers and solvent, the initiator or catalyst being initiallycharged or added with the monomers and the solvent. Variations such asinitial charging of the solvent in the reactor, addition of theinitiator or catalyst and then addition of the monomers, are possible.In addition, the polymerization can be operated in a continuous mode.Further addition of monomer and solvent during or at the end of thepolymerization is possible in all cases.

The polymerization time may vary within wide limits from a few minutesto a few hours. Typically, the polymerization is performed within aperiod of 10 minutes up to 8 hours, preferably 20 minutes to 4 hours. Itcan be performed either at standard pressure or at elevated pressure(from 1 to 10 bar).

It has been found that, surprisingly, the use of one or moresilalactones as functionalizing reagents can produce carboxyl-terminatedpolymers which do not have the disadvantages of the prior art.

The silalactones are compounds of the formula (III)

where

-   R¹, R² are the same or different and are each an H, alkyl, alkoxy,    cycloalkyl, cycloalkoxy, aryl, aryloxy, alkaryl, alkaryloxy, aralkyl    or aralkoxy radical which may contain one or more heteroatoms,    preferably O, N, S or Si,-   R³, R⁴ are the same or different and are each an H, alkyl,    cycloalkyl, aryl, alkaryl or aralkyl radical which may contain one    or more heteroatoms, preferably O, N, S or Si,-   A is a divalent organic radical which, as well as C and H, may    contain one or more heteroatoms, preferably O, N, S or Si,    where preferably-   R¹, R² are the same or different and are each an H, (C₁-C₂₄)-alkyl,    (C₁-C₂₄)-alkoxy, (C₃-C₂₄)-cycloalkyl, (C₃-C₂₄)-cycloalkoxy,    (C₆-C₂₄)-aryl, (C₆-C₂₄)-aryloxy, (C₆-C₂₄)-alkaryl,    (C₆-C₂₄)-alkaryloxy, (C₆-C₂₄)-aralkyl or (C₆-C₂₄)-aralkoxy radical    which may contain one or more heteroatoms, preferably O, N, S or Si,    and-   R³, R⁴ are the same or different and are each an H, (C₁-C₂₄)-alkyl,    (C₃-C₂₄)-cycloalkyl, (C₆-C₂₄)-aryl, (C₆-C₂₄)-alkaryl or    (C₆-C₂₄)-aralkyl radical which may contain one or more heteroatoms,    preferably O, N, S or Si.

Examples of compounds of the formula (III) are:

2,2-dimethyl-1-oxa-2-silacyclohexan-6-one (1),2,2,4-trimethyl-1-oxa-2-silacyclohexan-6-one (2),2,2,5-trimethyl-1-oxa-2-silacyclohexan-6-one (3),2,2,4,5-tetramethyl-1-oxa-2-silacyclohexan-6-one (4),2,2-diethyl-1-oxa-2-silacyclohexan-6-one (5),2,2-diethoxy-1-oxa-2-silacyclohexan-6-one (6),2,2-dimethyl-1,4-dioxa-2-silacyclohexan-6-one (7),2,2,5-trimethyl-1,4-dioxa-2-silacyclohexan-6-one (8),2,2,3,3-tetramethyl-1,4-dioxa-2-silacyclohexan-6-one (9),2,2-dimethyl-1-oxa-4-thia-2-silacyclohexan-6-one (10),2,2-diethyl-1-oxa-4-thia-2-silacyclohexan-6-one (11),2,2-diphenyl-1-oxa-4-thia-2-silacyclohexan-6-one (12),2-methyl-2-ethenyl-1-oxa-4-thia-2-silacyclohexan-6-one (13),2,2,5-trimethyl-1-oxa-4-thia-2-silacyclohexan-6-one (14),2,2-dimethyl-1-oxa-4-aza-2-silacyclohexan-6-one (15),2,2,4-trimethyl-1-oxa-4-aza-2-silacyclohexan-6-one (16),2,4-dimethyl-2-phenyl-1-oxa-4-aza-2-silacyclohexan-6-one (17),2,2-dimethyl-4-trimethylsilyl-1-oxa-4-aza-2-silacyclohexan-6-one (18),2,2-diethoxy-4-methyl-1-oxa-4-aza-2-silacyclohexan-6-one (19),2,2,4,4-tetramethyl-1-oxa-2,4-disilacyclohexane-6-one (20),3,4-dihydro-3,3-dimethyl-1H-2,3-benzoxasilin-1-one (21),2,2-dimethyl-1-oxa-2-silacyclopentan-5-one (22),2,2,3-trimethyl-1-oxa-2-silacyclopentan-5-one (23),2,2-dimethyl-4-phenyl-1-oxa-2-silacyclopentan-5-one (24),2,2-di(tert-butyl)-1-oxa-2-silacyclopentan-5-one (25),2-methyl-2-(2-propen-1-yl)-1-oxa-2-silacyclopentan-5-one (26),1,1-dimethyl-2,1-benzoxasilol-3(1H)-one (27),2,2-dimethyl-1-oxa-2-silacycloheptan-7-one (28).

The syntheses of such silalactones are described, for example, in U.S.Pat. No. 2,635,109; M. Wieber, M. Schmidt, Chemische Berichte 1963, 96(10), 2822-5; J. M. Wolcott, F. K. Cartledge, Journal of OrganicChemistry 1974, 39 (16), 2420-4; M. P. Sibi, J. W. Christensen,Tetrahedron Letters 1995, 36 (35), 6213-6; T. Linker, M. Maurer, F.Rebien, Tetrahedron Letters 1996, 37 (46), 8363-6; M. Shindo et al.,Angewandte Chemie, International Edition 2004, 43 (1), 104-6.

It has been found that the inventive end group-functionalized polymerscan be prepared by reaction of reactive ends of polymer chains withsilalactones and optional subsequent protonation of the carboxylate endgroup produced to give the carboxyl end group.

Thus, the invention also provides for the use of silalactones asfunctionalizing reagents for preparation of the inventive endgroup-functionalized polymers having end groups of the formula (I) or(II).

When polymers having very reactive nucleophilic ends of the polymerchains are reacted with compounds of the formula (III), the polymerchains cannot only be attached on the silicon atom of thefunctionalizing reagent; in addition, attachment may additionally occuron the carbonyl carbon atom. This leads to linear coupling of thepolymer chains (Scheme 1). In this case, a polymer mixture is present.Polymers having very reactive ends of the polymer chains are, forexample, diene homopolymers and diene copolymers, which are prepared bymeans of anionic polymerization or with coordination catalysts.

Coupling reactions of this kind may be desirable in some cases, in orderto increase the polydispersity and in this way to influence rheologicalproperties of the polymers, such as Mooney viscosity and cold flow. Inother cases, it may be advantageous to suppress the coupling reaction,in order to obtain a maximum number of functionalized ends of polymerchains, which should have a positive effect on the dynamic-mechanicalproperties of the vulcanizates containing these polymers.

It has now been found that, surprisingly, the coupling reactionaccording to Scheme 1 can be prevented virtually completely (<5% byweight based on the total amount of polymer) when polymers having veryreactive nucleophilic ends of the polymer chains are reacted in a firststep with a reagent which leads to polymers having silanol or silanolateend groups and, in a second step, these polymers having silanol orsilanolate end groups are allowed to react with compounds of the formula(III) (Scheme 2). It is likewise possible to set a desired level ofcoupling in a controlled manner by, in a first step, reacting not all ofthe very reactive nucleophilic ends of the polymer chains with a reagentwhich leads to polymers having silanol or silanolate end groups.

Reagents of this kind which are used in the first step can lead directlyor indirectly (for example via a subsequent hydrolysis of Si—Cl groups)to silanol or silanolate end groups. Preference is given, however, toreagents which give silanolate end groups in a direct reaction. Veryparticular preference is given to cyclosiloxanes of the formula (IV)

where R⁵, R⁶ in Scheme 2 and in formula (IV) are the same or differentand are each an H, alkyl, cycloalkyl, aryl, alkaryl or aralkyl radicalwhich may contain one or more heteroatoms, preferably O, N, S or Si.

Preference is given to hexamethylcyclotrisiloxane,octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane anddodecamethylcyclohexasiloxane, and to mixtures of cyclosiloxanes ofdifferent ring size.

The intermediates obtainable in Scheme 2 can be isolated by the methodsknown to those skilled in the art.

The inventive end group-functionalized polymers preferably have meanmolar masses (number-average, M_(n)) of 10 000 to 2 000 000 g/mol,preferably of 100 000 to 1 000 000 g/mol, and glass transitiontemperatures of −110° C. to +20° C., preferably of −110° C. to 0° C.,and Mooney viscosities [ML 1+4 (100° C.)] of 10 to 200, preferably of 30to 150, Mooney units.

The invention further provides a process for preparing the inventive endgroup-functionalized polymers, in which one or more compounds of theformula (III) are added, as a pure substance, solution or suspension, togive polymers having reactive ends of the polymer chains. The additionpreferably follows conclusion of the polymerization, but may alsoprecede complete monomer conversion. The reaction of compounds of theformula (III) with polymers having reactive ends of the polymer chainsis effected at the temperatures customarily used for the polymerization.The reaction times for the reaction of compounds of the formula (III)with the reactive ends of the polymer chains may be between a fewminutes and several hours.

The amount of these compounds can be selected such that all the reactiveends of the polymer chains react with compounds of the formula (III), orit is possible to use a deficiency of these compounds. The amounts ofthe compounds of the formula (III) used may cover a wide range. Thepreferred amounts are within a range from 0.005 to 2% by weight, morepreferably within a range from 0.01 to 1% by weight, based on the amountof polymer.

The invention further provides for the reaction of polymers havingcarbanionic chain ends (obtained from the anionic polymerization or thepolymerization with coordination catalysts) first with cyclosiloxanes ofthe formula (IV) and, in a next step, the reaction of thesilanolate-terminated polymers obtained from the first step withcompounds of formula (III) to give carboxylate-terminated polymers. Thecyclosiloxanes of the formula (IV) can be used in pure form or as amixture of different cyclosiloxanes. The amount of the cyclosiloxanescan be selected such that all the reactive ends of the polymer chainsreact with cyclosiloxanes of the formula (IV), or it is possible to usea deficiency of these compounds. The amounts of the cyclosiloxanes ofthe formula (IV) used may cover a wide range. The preferred amounts arewithin a range from 0.002 to 4% by weight, more preferably within arange from 0.005 to 2% by weight, based on the amount of polymer. Theamount of compounds of the formula (III) in the subsequent step isideally selected such that any and all carbanionic ends of polymerchains present and all silanolate-terminated ends of polymer chainsreact with compounds of the formula (III). The preferred ratio ofsilalactone to cyclosiloxane is 20:1 to 1:1, particular preference beinggiven to a ratio of 10:1 to 1:1, very particular preference to a ratioof 3:1 to 1:1.

In addition to compounds of the formula (III) and cyclosiloxanes of theformula (IV), it is also possible to use the coupling reagents typicalof anionic diene polymerization for reaction with the reactive ends ofpolymer chains. Examples of such coupling reagents are silicontetrachloride, methyltrichiorosilane, dimethyldichlorosilane, tintetrachloride, dibutyltin dichloride, tetraalkoxysilanes, ethyleneglycol diglycidyl ether, 1,2,4-tris(chloromethyl)benzene. Such couplingreagents can be added prior to, together with or after the compounds ofthe formula (III).

After addition of compounds of the formula (III) and optionally ofcoupling reagents, before or during the workup of the inventivesilane-containing, carboxylate-terminated polymers, preference is givento adding the customary ageing stabilizers, such as sterically hinderedphenols, aromatic amines, phosphites, thioethers. In addition, it ispossible to add the customary extender oils used for diene rubbers, suchas DAE (Distillate Aromatic Extract), TDAE (Treated Distillate AromaticExtract), MES (Mild Extraction Solvates), RAE (Residual AromaticExtract), TRAE (Treated Residual Aromatic Extract), naphthenic and heavynaphthenic oils. It is also possible to add fillers, such as carbonblack and silica, rubbers and rubber auxiliaries.

The solvent can be removed from the polymerization process by thecustomary methods, such as distillation, stripping with steam orapplication of reduced pressure, optionally at elevated temperature.

The invention further provides for the use of the inventive endgroup-functionalized polymers for production of vulcanizable rubbercompositions.

These vulcanizable rubber compositions preferably comprise furtherrubbers, fillers, rubber chemicals, processing aids and extender oils.

Additional rubbers are, for example, natural rubber and syntheticrubbers. If present, the amount thereof is typically within the rangefrom 0.5 to 95% by weight, preferably within the range from 10 to 80% byweight, based on the total amount of polymer in the mixture. The amountof rubbers additionally added is again guided by the respective end useof the inventive mixtures. Examples of synthetic rubbers of this kindare BR (polybutadiene), acrylic acid-alkyl ester copolymers, IR(polyisoprene), E-SBR (styrene-butadiene copolymers prepared by emulsionpolymerization), S-SBR (styrene-butadiene copolymers prepared bysolution polymerization), IIR (isobutylene-isoprene copolymers), NBR(butadiene-acrylonitrile copolymers), HNBR (partly hydrogenated or fullyhydrogenated NBR rubber), EPDM (ethylene-propylene-diene terpolymers)and mixtures of these rubbers. For the production of car tyres,particularly natural rubber, E-SBR and S-SBR having a glass transitiontemperature above −60° C., polybutadiene rubber which has a high ciscontent (>90%) and has been prepared with catalysts based on Ni, Co, Tior Nd, and polybutadiene rubber having a vinyl content of up to 80% andmixtures thereof are of interest.

Useful fillers for the inventive rubber compositions include all knownfillers used in the rubber industry. These include both active andinactive fillers.

The following should be mentioned by way of example:

-   -   finely divided silicas, produced, for example, by precipitation        of solutions of silicates or flame hydrolysis of silicon halides        having specific surface areas of 5-1000, preferably 20-400, m²/g        (BET surface area) and having primary particle sizes of 10-400        nm. The silicas may optionally also be present as mixed oxides        with other metal oxides, such as oxides of Al, Mg, Ca, Ba, Zn,        Zr, Ti;    -   synthetic silicates, such as aluminium silicate, alkaline earth        metal silicates such as magnesium silicate or calcium silicate,        having BET surface areas of 20-400 m²/g and primary particle        diameters of 10-400 nm;    -   natural silicates, such as kaolin, montmorillonite and other        naturally occurring silicas;    -   glass fibres and glass fibre products (mats, strands) or glass        microspheres;    -   metal oxides, such as zinc oxide, calcium oxide, magnesium        oxide, aluminium oxide;    -   metal carbonates, such as magnesium carbonate, calcium        carbonate, zinc carbonate;    -   metal hydroxides, for example aluminium hydroxide, magnesium        hydroxide;    -   metal sulphates, such as calcium sulphate, barium sulphate;    -   carbon blacks: The carbon blacks to be used here are carbon        blacks produced by the lamp black, channel black, furnace black,        gas black, thermal black, acetylene black or light arc process        and have BET surface areas of 9-200 m²/g, for example SAF,        ISAF-LS, ISAF-HM, ISAF-LM, ISAF-HS, CF, SCF, HAF-LS, HAF,        HAF-HS, FF-HS, SPF, XCF, FEF-LS, FEF, FEF-HS, GPF-HS, GPF, APF,        SRF-LS, SRF-LM, SRF-HS, SRF-HM and MT carbon blacks, or ASTM        N110, N219, N220, N231, N234, N242, N294, N326, N327, N330,        N332, N339, N347, N351, N356, N358, N375, N472, N539, N550,        N568, N650, N660, N754, N762, N765, N774, N787 and N990 carbon        blacks;    -   rubber gels, especially those based on BR, E-SBR and/or        polychloroprene having particle sizes of 5 to 1000 nm.

The fillers used are preferably finely divided silicas and/or carbonblacks.

The fillers mentioned can be used alone or in a mixture. In aparticularly preferred embodiment, the rubber compositions comprise, asfillers, a mixture of light-coloured fillers, such as finely dividedsilicas, and carbon blacks, the mixing ratio of light-coloured fillersto carbon blacks being 0.01:1 to 50:1, preferably 0.05:1 to 20:1.

The fillers are used here in amounts in the range from 10 to 500 partsby weight based on 100 parts by weight of rubber. Preference is given tousing amounts within a range from 20 to 200 parts by weight.

In a further embodiment of the invention, the rubber compositions alsocomprise rubber auxiliaries which, for example, improve the processingproperties of the rubber compositions, serve to crosslink the rubbercompositions, improve the physical properties of the vulcanizatesproduced from the inventive rubber compositions for the specific end usethereof, improve the interaction between rubber and filler, or serve forattachment of the rubber to the filler.

Rubber auxiliaries are, for example, crosslinker agents, for examplesulphur or sulphur-supplying compounds, and also reaction accelerators,ageing stabilizers, heat stabilizers, light stabilizers, antiozonants,processing aids, plasticizers, tackifiers, blowing agents, dyes,pigments, waxes, extenders, organic acids, silanes, retardants, metaloxides, extender oils, for example DAE (Distillate Aromatic Extract),TDAE (Treated Distillate Aromatic Extract), MES (Mild ExtractionSolvates), RAE (Residual Aromatic Extract), TRAE (Treated ResidualAromatic Extract), naphthenic and heavy naphthenic oils and activators.

The total amount of rubber auxiliaries is within the range from 1 to 300parts by weight, based on 100 parts by weight of overall rubber.Preference is given to using amounts within a range from 5 to 150 partsby weight of rubber auxiliaries.

The vulcanizable rubber compositions can be produced in a one-stage orin a multistage process, preference being given to 2 to 3 mixing stages.For example, sulphur and accelerator can be added in a separate mixingstage, for example on a roller, preferred temperatures being in therange from 30° C. to 90° C. Preference is given to adding sulphur andaccelerator in the last mixing stage.

Examples of equipment suitable for the production of the vulcanizablerubber compositions include rollers, kneaders, internal mixers or mixingextruders.

Thus, the invention further provides vulcanizable rubber compositionscomprising end group-functionalized polymers having end groups of theformula (I) or (II).

The invention further provides for the use of the inventive vulcanizablerubber compositions for production of rubber vulcanizates, especiallyfor the production of tyres, especially tyre treads, having particularlylow rolling resistance coupled with high wet skid resistance andabrasion resistance.

The inventive vulcanizable rubber compositions are also suitable forproduction of mouldings, for example for the production of cablesheaths, hoses, drive belts, conveyor belts, roll covers, shoe soles,gasket rings and damping elements.

The examples which follow serve to illustrate the invention but have nolimiting effect.

EXAMPLES Example 1: Synthesis of Styrene-Butadiene Copolymer,Unfunctionalized (Comparative Example)

An inertized 20 l reactor was charged with 8.5 kg of hexane, 1185 g of1,3-butadiene, 315 g of styrene, 8.6 mmol of2,2-bis(2-tetrahydrofuryl)propane and 11.3 mmol of butyllithium, and thecontents were heated to 60° C. Polymerization was effected whilestirring at 60° C. for 25 minutes, Subsequently, 11.3 mmol of cetylalcohol were added to cap the anionic ends of the polymer chains, therubber solution was discharged and stabilized by addition of 3 g ofIrganox® 1520 (2,4-bis(octylthiomethyl)-6-methylphenol), and the solventwas removed by stripping with steam. The rubber crumbs were dried at 65°C. under reduced pressure.

Example 2: Synthesis of Silanolate-Terminated Styrene-ButadieneCopolymer by Reaction with Cyclosiloxane (Comparative Example)

The procedure was as in Example 1. In place of the cetyl alcohol,however, an amount of hexamethylcyclotrisiloxane equimolar to that ofbutyllithium was added (as a solution in cyclohexane) and the reactorcontents were then heated to 60° C. for a further 20 minutes.

Example 3: Synthesis of Silane-Containing Carboxyl-TerminatedStyrene-Butadiene Copolymer by Reaction with Cyclosiloxane and thenSilalactone (Inventive)

The procedure was as in Example 2. 20 minutes after addition of thehexamethylcyclotrisiloxane, an amount of2,2-dimethyl-1-oxa-4-thia-2-silacyclohexan-6-one equimolar to that ofbutyllithium and hexamethylcyclotrisiloxane was added (as a solution intoluene) and the mixture was heated to 60° C. for a further 20 minutes.

Example 4: Synthesis of Silane-Containing Carboxyl-TerminatedStyrene-Butadiene Copolymer Having a Tertiary Amino Group at the Startof the Chain by Reaction with Cyclosiloxane and then Silalactone(Inventive)

The procedure was as in Example 3. Prior to addition of thebutyllithium, however, an amount of pyrrolidine equimolar to that ofbutyllithium was added.

Example 5: Synthesis of Silane-Containing Hydroxyl-TerminatedStyrene-Butadiene Copolymer by Reaction with 1-Oxa-2-Silacycloalkanes(Comparative Example)

The procedure was as in Example 2. In place of thehexamethylcyclotrisiloxane, however, an amount of2,2,4-trimethyl-1-oxa-4-aza-2-silacyclohexane equimolar to that ofbutyllithium was added (as a solution in hexane).

The polymer properties of the styrene-butadiene copolymers from Examples1-5 are summarized in Table 1. It is apparent from Table 1 that theinventive silane-containing carboxyl-terminated polymers of Examples 3and 4, with the same molecular weight and polydispersity level as thepolymers of Comparative Examples 1, 2 and 5, have much higher Mooneyviscosities and much reduced cold flow values. Low cold flow values areadvantageous, since the corresponding rubbers have a lesser tendency toflow and hence improved dimensional stability in the course of storage.

Examples 6 a-e: Rubber Compositions

Tyre tread rubber compositions comprising the styrene-butadienecopolymers of Examples 1-5 were produced. The constituents are listed inTable 2. The rubber compositions (apart from sulphur and accelerator)were produced in a 1.5 l kneader. The sulphur and acceleratorconstituents were subsequently mixed in on a roller at 40° C.

TABLE 1 Properties of the styrene-butadiene copolymers of Examples 1-5Styrene Functionalizing Vinyl content^(a)) content^(a)) Tg^(b)) M_(n)^(c)) ML1 + 4^(d)) Cold flow^(e)) SSBR from Ex. reagent [% by wt.] [% bywt.] [° C.] [kg/mol] M_(w)/M_(n) ^(c)) [ME] [mg/min] 1 — 51.5 20.9 −23244 1.10 42 21 (comparative) 2 hexamethyl- 50.6 21.3 −24 239 1.10 41 21(comparative) cyclotrisiloxane 3 1. hexamethyl- 50.7 21.0 −24 246 1.0979 0 (inventive) cyclotrisiloxane 2. silalactone 4 1. hexamethyl- 49.921.9 −24 183 1.22 56 9 (inventive) cyclotrisiloxane 2. silalactone 51-oxa-2- 50.9 21.5 −23 220 1.15 37 25 (comparative) silacycloalkane^(a))determination of vinyl and styrene contents by FTIR^(b))determination of glass transition temperature by DSC^(c))determination of molar mass M_(n) and polydispersity M_(w)/M_(n) byGPC (PS calibration) ^(d))determination of Mooney viscosity at 100° C.^(e))determination of cold flow at 50° C.

TABLE 2 Constituents of the tyre tread rubber compositions (figures inphr: parts by weight per 100 parts by weight of rubber) ComparativeComparative Inventive Inventive Comparative Example Example ExampleExample Example 6a 6b 6c 6d 6e styrene-butadiene copolymer from Example1 70 0 0 0 0 styrene-butadiene copolymer from Example 2 0 70 0 0 0styrene-butadiene copolymer from Example 3 0 0 70 0 0 styrene-butadienecopolymer from Example 4 0 0 0 70 0 styrene-butadiene copolymer fromExample 5 0 0 0 0 70 high-cis polybutadiene 30 30 30 30 30 (BUNA ™ CB 24from Lanxess Deutschland GmbH) silica (Ultrasil ® 7000) 90 90 90 90 90carbon black (Vulcan ® J/N 375) 7 7 7 7 7 TDAE oil (Vivatec 500) 36.336.3 36.3 36.3 36.3 processing aid (Aflux 37) 3 3 3 3 3 stearic acid(Edenor C 18 98-100) 1 1 1 1 1 ageing stabilizer 2 2 2 2 2 (Vulkanox ®4020/LG from Lanxess Deutschland GmbH) ageing stabilizer 2 2 2 2 2(Vulkanox ® HS/LG from Lanxess Deutschland GmbH) zinc oxide (Rotsiegelzinc white) 3 3 3 3 3 wax (Antilux 654) 2 2 2 2 2 silane (SI 69 ® fromEvonik) 7.2 7.2 7.2 7.2 7.2 diphenylguanidine (Rhenogran DPG-80) 2.752.75 2.75 2.75 2.75 sulfenamide (Vulkacit ® NZ/EGC from LanxessDeutschland GmbH) 1.6 1.6 1.6 1.6 1.6 sulphur (Chancel 90/95 groundsulphur) 1.6 1.6 1.6 1.6 1.6 sulfonamide (Vulkalent ® E/C) 0.2 0.2 0.20.2 0.2

Examples 7 a-e: Vulcanizate Properties

The tyre tread rubber compositions of Examples 6a-e according to Table 2were vulcanized at 160° C. for 20 minutes. The properties of thecorresponding vulcanizates are listed in Table 3 as Examples 7a-e. Thevulcanizate properties of the vulcanized sample from Comparative Example7a comprising the unfunctionalized styrene-butadiene copolymer are giventhe index 100. All values greater than 100 in Table 3 mean acorresponding percentage improvement in the respective test property.

TABLE 3 Vulcanizate properties Comparative Comparative InventiveInventive Comparative Example Example Example Example Example 7a 7b 7c7d 7e Styrene-butadiene copolymer in the vulcanizate: styrene-butadienecopolymer from Example 1 X styrene-butadiene copolymer from Example 2 Xstyrene-butadiene copolymer from Example 3 X styrene-butadiene copolymerfrom Example 4 X styrene-butadiene copolymer from Example 5 XVulcanizate properties: tan δ at 0° C. (dynamic damping at 10 Hz) 100112 125 125 115 tan δ at 60° C. (dynamic damping at 10 Hz) 100 110 143145 117 tan δ maximum (MTS amplitude sweep at 1 Hz, 60° C.) 100 115 134139 117 ΔG* (G*@0.5%-G*@15% from MTS amplitude sweep) 100 159 254 255189 [MPa] Resilience at 60° C. [%] 100 113 118 121 114 Abrasion (DIN53516) [mm³] 100 119 135 130 113

The resilience at 60° C., the dynamic damping tan δ at 6000, the tan δmaximum in the amplitude sweep and the module difference ΔG* between lowand high strain in the amplitude sweep are indicators of rollingresistance in the tyre. As apparent from Table 3, the vulcanizates ofInventive Examples 7c and 7d feature particularly high improvements inthese rolling resistance-relevant properties.

The dynamic damping tan δ at 0° C. is an indicator of the wet skidresistance of the tyre. As apparent from Table 3, the vulcanizates ofInventive Examples 7c and 7d feature particularly high improvements inthis wet skid-relevant property.

The DIN abrasion is an indicator of the abrasion resistance of the tyretread. As apparent from Table 3, the vulcanizates of Inventive Examples7c and 7d feature particularly high improvements in this property.

What is claimed is:
 1. End group-functionalized polymers comprising apolymer chain terminated by a silane-containing carboxyl group of theformula (I)

wherein the silane containing carboxyl group is bonded with the polymerchain via one or more divalent structural elements of the formula (V)

where R is H, R¹, R² are the same or different and are each an H, alkyl,alkoxy, cycloalkyl, cycloalkoxy, aryl, aryloxy, alkaryl, alkaryloxy,aralkyl, or aralkoxy radical R³, R⁴ are the same or different and areeach an H, alkyl, cycloalkyl, aryl, alkaryl or aralkyl radical, A is adivalent organic radical, n=3-6, and R⁵, R⁶ are the same or differentand are each an H, alkyl, cycloalkyl, aryl, alkaryl or aralkyl radicalwherein the polymers are diene polymers or diene copolymers.
 2. The endgroup-functionalized polymers according to claim 1, wherein the polymeris obtained by reaction of reactive ends of the polymer chain with oneor more silalactone functionalizing reagents, wherein the silalactonesare compounds of the formula (III)


3. The end group-functionalized polymers according to claim 2, wherein:any alkyl, alkoxy, cycloalkyl, cycloalkoxy, aryl, aryloxy, alkaryl,alkaryloxy, aralkyl, aralkoxy, or divalent organic radical may containone or more heteroatoms; the silalactones are compounds of the formula(III)

and the one or more divalent structural elements of the formula (V) arederived from cyclosiloxanes of the formula (IV)


4. The end group-functionalized polymers according to claim 3, wherein:the heteroatoms are O, N, S and Si; the cyclosiloxanes are a member ofthe group consisting of hexamethylcyclotrisiloxane,octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, ordodecamethylcyclcohexasiloxane; the silalactones comprise one or more of2,2-diethyl-1-oxa-2-silacyclohexan-6-one,2,2,4-trimethyl-1-oxa-2-silacyclohexan-6-one,2,2,5-trimethyl-1-oxa-2-silacyclohexan-6-one,2,2,4,5-tetramethyl-1-oxa-2-silacyclohexan-6-one,2,2-diethyl-1-oxa-2-silacyclohexan-6-one,2,2-diethoxy-1-oxa-2-silacyclohexan-8-one,2,2-dimethyl-1,4-dioxa-2-silacyclohexan-6-one,2,2,5-trimethyl-1,4-dioxa-2-silacyclohexan-6-one,2,2,3,3-tetramethyl-1,4-dioxa-2-silacyclohexan-6-one,2,2-dimethyl-1-oxa-4-thia-2-silacyclohexan-6-one,2,2-diethyl-1-oxa-4-thia-2-silacyclohexan-6-one,2,2-diphenyl-1-oxa-4-thia-2-silacyclohexan-6-one,2-methyl-2-ethenyl-1-oxa-4-thia-2-silacyclohexan-6-one,2,2,5-trimethyl-1-oxa-4-thia-2-silacyclohexan-8-one,2,2-dimethyl-1-oxa-4-aza-2-silacyclohexan-6-one,2,2,4-trimethyl-1-oxa-4-aza-2-silacyclohexan-6-one,2,4-dimethyl-2-phenyl-1-oxa-4-aza-2-silacyclohexan-6-one, 2,2-dimethyl-4trimethylsilyl-1-oxa-4-aza-2-silacyclohexan-6-one,2,2-diethoxy-4-methyl-1-oxa-4-aza-2-silacyclohexan-6-one,2,2,4,4-tetramethyl-1-oxa-2,4-disilacyclohexane-6-one,3,4-dihydro-3,3-dimethyl-1H-2,3-benzoxasilin-1-one,2,2-dimethyl-1-oxa-2-silacyclopentan-5-one,2,2,3-trimethyl-1-oxa-2-silacyclopentan-5-one,2,2-dimethyl-4-phenyl-1-oxa-2-silacyclopentan-5-one,2,2-di(tert-butyl)-1-oxa-2-silacyclopentan-5-one,2-methyl-2-(2-propen-1-yl)-1-oxa-2-silacyclopentan-5-one,1,1-dimethyl-2,1-benzoxasilol-3(1H)-one, and2,2-dimethyl-1-oxa-2-silacycloheptan-7-one; the polymers comprise atleast one of polybutadiene, polyisoprene, butadiene-isoprene copolymer,butadiene-styrene copolymer, isoprene-styrene copolymer, andbutadiene-isoprene-styrene terpolymer; and the polymers have mean molarmasses of 100,000 to 1,000,000 g/mol, and glass transition temperaturesof −110° C. to 0° C.
 5. The end group-functionalized polymers accordingto claim 1, wherein the polymers have mean molar masses of 10,000 to2,000,000 g/mol.
 6. The end group-functionalized polymers according toclaim 1, wherein the polymers have glass transition temperatures of−110° C. to +20° C.
 7. A process for preparing the endgroup-functionalized polymers according to claim 1, the processcomprising adding one or more silalactones to polymers having reactiveends on the polymer chain.
 8. The process according to claim 7, furthercomprising adding the silalactones to the polymers after completion ofpolymerization.
 9. The process according to claim 7, further comprisingusing an excess or a stoichiometric amount or a deficiency ofsilalactones, based on the amount of polymer.
 10. The process accordingto claim 9, wherein the amount of silalactones is from 0.005 to 2% byweight, based on the amount of polymer.
 11. The process according toclaim 7, wherein prior to addition of the silalactones, the processfurther comprises: polymerizing monomers to form polymer chains havingreactive chain ends, and reacting reactive chain ends withcyclosiloxanes of the formula (IV)

where n=3-6, and where R⁵, R⁶ in formula (IV) are the same or differentand are each an H, alkyl, cycloalkyl, aryl, alkaryl or aralkyl radical.12. The process according to claim 11, further comprising reacting thereactive chain ends with 0.002 to 4% by weight of the cyclosiloxanes ofthe formula (IV) based on the amount of polymer.
 13. The processaccording to claim 11, wherein a ratio of silalactone to cyclosiloxaneis from 20:1 to 1:1.
 14. Vulcanizable rubber compositions comprising: a)end group-functionalized polymers according to claim 1, and b) ageingstabilizers, oils, fillers, rubbers and/or further rubber auxiliaries.15. Mouldings produced from vulcanizable rubber compositions comprisingthe end group-functionalized polymers according to claim 1.